In midst of drought, fertilizer carryover evidenced

Caroline Booth Lara | Aug 18, 2006

For those in search of some good news related to the drought: If you put fertilizer on pastures this spring and haven’t had much rain or grass growth, it’s possible the fertilizer is still there. That might mean savings when it’s time to plant again.

“We are seeing a lot more carryover in samples than we anticipated,” says Eddie Funderburg, a soil and crops specialist at the Noble Foundation in Ardmore, Okla.

Phosphorus and potassium are very likely still in the soil, Funderburg says, because they are lost through crop removal or erosion.

“Also, you essentially only lose nitrogen through crop uptake or leaching,” Funderburg says. “Since we haven’t had any rainfall, we figure it’s still there if you put it out.”

The nitrogen source will have an effect on the amount of carryover, however. Funderburg says if urea was applied to the soil surface without incorporation and there was no rain for two weeks after, initial losses could be as high as 40 percent. With ammonium nitrate or ammonium sulfate, atmospheric losses would be minimal.

To determine if pastures have carryover fertilizer, take a soil sample. Funderburg recommends both 0- to 6-inch and 6- to 12-inch samples.

“The deep samples will be hard to pull at this time, but they are worth it,” he says.

Funderburg’s normal recommendation for wheat pasture is 100 to 150 pounds of actual nitrogen per acre. At current nitrogen prices of around 40 cents per pound, determining carryover and potentially having to apply less nitrogen to winter pasture is appealing.

“Keep it in mind — you may be able to save money where you might not have expected it,” he says.